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RESEARCH ARTICLE

Using mathematical modelling to help explain the differential increase in HIV incidence in New South Wales, Victoria and Queensland: importance of other sexually transmissible infections

Alexander Hoare A , David P. Wilson A B , David G. Regan A , John Kaldor A and Matthew G. Law A
+ Author Affiliations
- Author Affiliations

A National Centre in HIV Epidemiology and Clinical Research, Faculty of Medicine, University of New South Wales, Level 2, 376 Victoria Street, Sydney, NSW 2010, Australia.

B Corresponding author. Email: dwilson@nchecr.unsw.edu.au

Sexual Health 5(2) 169-187 https://doi.org/10.1071/SH07099
Submitted: 17 December 2007  Accepted: 16 April 2008   Published: 2 June 2008

Abstract

Background: Since 1999 there has been an increase in the number of HIV diagnoses in Australia, predominantly among men who have sex with men (MSM), but the magnitude of increase differs between states: ~7% rise in New South Wales, ~96% rise in Victoria, and ~68% rise in Queensland. Methods: Epidemiological, clinical, behavioural and biological data were collated into a mechanistic mathematical model to explore possible reasons for this increase in HIV notifications in MSM. The model was then used to make projections to 2015 under various scenarios. Results: The model suggests that trends in clinical and behavioural parameters, including increases in unprotected anal intercourse, cannot explain the magnitude of the observed rise in HIV notifications, without a substantial increase in a ‘transmission-increasing’ factor. We suggest that a highly plausible biological factor is an increase in the prevalence of other sexually transmissible infections (STI). It was found that New South Wales required an ~2-fold increase in other STI to match the data, Victoria needed an ~11-fold increase, and Queensland required an ~9-fold increase. This is consistent with observed trends in Australia for some STI in recent years. Future projections also indicate that the best way to control the current rise in HIV notifications is to reduce the prevalence of other STI and to promote condom use, testing for HIV, and initiation of early treatment in MSM diagnosed during primary infection. Conclusions: Our model can explain the recent rise in HIV notifications with an increase in the prevalence of other STI. This analysis highlights that further investigation into the causes and impact of other STI is warranted in Australia, particularly in Victoria.

Additional keywords: Australia, men who have sex with men.


Acknowledgements

The authors thank the members of the Reference Group that provided advice and guidance through the development of this report. Members of the Reference Group, and the bodies they represented, were: Professor Frank Bowden, HIV/AIDS and STI Subcommittee of the Ministerial Advisory Committee on AIDS, Sexual Health and Hepatitis; Ms Sharon Flanagan and Ms Karen Fox, Australian Government Department of Health and Ageing; Associate Professor John Imrie, National Centre in HIV Social Research, University of New South Wales; Mr Philip Keen, AIDS Council of New South Wales; Dr Rosemary Lester, Communicable Diseases Network Australia; Dr Kelly Shaw, Blood Borne Virus Surveillance System; and Mr Bill Whittaker, National Association of People living With HIV/AIDS. The authors also thank the following colleagues and collaborators at the National Centre in HIV Epidemiology and Clinical Research for making data available, and also for numerous discussions and advice on interpretation: Dr Handan Wand, Ms Linda Gelgor, Ms Kathleen Falster, Professor Andrew Grulich, Associate Professor Anthony Kelleher, Ms Ann McDonald, Ms Melanie Middleton and Dr Garrett Prestage. The National Centre in HIV Epidemiology and Clinical Research is funded by the Australian Government Department of Health and Ageing, and is affiliated with the Faculty of Medicine, University of New South Wales. Dr David Wilson is funded by a Vice Chancellor’s Fellowship from the University of New South Wales and by grant number DP0771620 from the Australian Research Council; Mr Alex Hoare is funded by a University Postgraduate Award from the University of New South Wales; Dr David Regan is funded by grant number 358425 from the Australian National Health and Medical Research Council; Associate Professor Matthew Law is funded by grant numbers 1-U01-AI6994-01, 1-U01-AI068641, 1-U01-A1069907-01 and 5-U19-AI05371 from the National Institutes of Health, USA.


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